Most plants require well-drained soil and do not tolerate wet or soggy conditions. When starting a new garden bed, soil drainage issues must be addressed before you ever begin planting. Few soils have perfect drainage. Clay soils may hold on to too much moisture or become so compacted that no water can permeate them. Sandy soils may drain too quickly so there is not enough time for plants to absorb needed water. Testing the drainage of your soil allows you to recognize any problem and fix it.
Dig a hole 12-inches deep in the area you are planning to turn to a garden. Make the hole at least 6-inches wide.
Fill the hole with water. Check it every 30 minutes for the first hour after filling, then once per hour thereafter until the water has drained out.
Amend the garden bed with organic matter, such as compost and peat moss, if the water drains out in 30 minutes or less. This indicates sandy soil that needs organic matter in order to hold moisture longer.
Amend with coarse shredded bark and compost, or install a French drain under, beds that take between six and 24 hours to drain. This indicates clay soil which needs to be loosened in order to drain properly. If it takes 24 hours or longer to drain, a drain is a necessity, according to Colorado State University Extension specialists. A French drain, is a trench filled with crushed rock or gravel that allows water to drain downhill to an outlet.